1. Field of the Invention
This invention relates to inflation and automatic pressure relief valves for an inflatable cuff on an endotracheal tube.
2. The Prior Art
Endotracheal tubes are well-known in the medical arts and are used extensively for the ventilation of a patient's lungs particularly during periods of anesthesia. The endotracheal tube consists of a tube having an open end which is inserted into the patient's tracheal passage and is connected at the other end to an anesthetic gas delivery system. In order to function properly and provide suitable inflation of the lungs, it is necessary that the tracheal passage surrounding the endotracheal tube be sealed to prevent the escape of gases particularly during the inflation phase of the breathing cycle.
Historically, sealing of the tracheal passage has been accomplished by an inflatable cuff which is disposed as an annulus recessed from the tip of the endotracheal tube. The endotracheal tube includes a small cuff inflation lumen and an enlarged main lumen for the anesthesia gas delivery.
Early devices included a relatively unyielding inflatable cuff which, upon inflation, tended to require a relatively high pressure in order to adequately seal the tracheal passage against gas leakage. However, these relative high pressures exceeded the blood pressure within the surrounding tissue such that the tissue was deprived of an adequate blood supply resulting in ischemia and even necrosis of the underlying tissue. In some instances an over pressure would even result in stretching of the tracheal passage tissue.
Tissue damage and throat discomfort to the patient led to the development of lower pressure cuffs which were fabricated from a relatively pliant material and were designed to contact the internal surface of the tracheal passage over a greater surface area. Appropriate sealing of the tracheal passage could then be accomplished at a lower cuff inflation pressure.
The introduction of this latter improvement in endotracheal tubes has resulted in a further problem with respect to maintaining the appropriate cuff pressure. In particular, it has been discovered that the pliant cuff material acts as a semipermeable membrane toward the anesthetic gases. For example, anesthetic gases are generally constituted on the basis of about 60% nitrous oxide and 40% oxygen. Meanwhile, the cuff has been inflated with air (approximately 78% nitrogen and 20% oxygen). Since nitrous oxide is approximately 60% to 70% more difusable through a semi-permeable membrane when compared to nitrogen, a high proportion of nitrous oxide has been found to diffuse into the cuff and thereby increase the pressure.
It has been found that pressures as high as 350 milliimeters of mercury have been recorded whereas the normal blood pressure is approximately 120 millimeters of mercury. Accordingly, the higher pressure in the cuff results in ischemia of the underlying tissue.
In view of the foregoing problem anesthesiologists have been known to inflate the cuff with the anesthetic gas, however, if the anesthetic gas is changed during the procedure, then the inflation gas within the cuff must also be changed.
It has also been known to incorporate an externally located balloon in gaseous communication with the cuff so as to receive excess gases absorbed into the cuff. The balloon is enclosed within a protective cover. Excessive quantities of gases received by the balloon cause the balloon to swell or expand to the limits imposed by the protective cover and thereby cause the pressure within the cuff to increase. This problem arises more frequently when restrictive areas in the trachea require a smaller diameter endotracheal tube and the cuff must, therefore, be inflated with a greater quantity of gas to compensate for the smaller diameter endotracheal tube.
In view of the foregoing, what is needed is an adjustable pressure relief valve which can be connected to the inflation lumen so as to relieve excess pressures that develop within the cuff. The relief valve should be adjustable to accomodate various pressure settings. Advantageously, the relief valve should include valve means for receiving the inflation gas for the cuff. The apparatus may also be inexpensively produced so as to be readily disposable. Such an invention is disclosed herein.